Blockable bone plate

ABSTRACT

The blockable bone plate consists of a plurality of plate members which are connected to each other via webs. A screw hole is provided in at least some plate members, preferably in each plate member. The screw hole is surrounded by a spherical countersink on the upper surface of the plate. Provided internally in the screw hole there is an engagement contour which consists of contour valleys and contour peaks partially running in a horizontal and radial peripheral direction on the wall of the screw hole. The engagement contour is preferably produced by milling and has for example a pointed, round, trapezoidal or serrated configuration. A blocking thread is provided under the screw head of the screw intended for blocking. As the screw is screwed in, the blocking thread engages in the engagement contour. The particular advantages lie in increased security against the screw coming loose and in the possibility of also inserting the screw through the plate at an inclination. Furthermore, a bone plate is proposed which has the shape of an arc of a circle in the longitudinal axis of the plate and which requires less bending, particularly on the human lower jaw, and adapts to the bone in a more ideal manner.

FIELD OF APPLICATION OF THE INVENTION

The present invention relates to a blockable bone plate with securedbone screws which serve in particular as a reconstruction system for themaxillofacial region of the human skull, for example for the lower jaw.For the time being, the shorter terms “plate”, “screw” and “plate-screwconnection” are used. Such plates are used, for example, to strengthenweakened and damaged bone structures. In the case of large continuitydefects, the plates have to provide stability over long periods of timeand take up the loads which the missing bone would have supported.Plates of this type consist in their simplest form of a straightelongate branch with a multiplicity of plate members, in each of which ascrew hole is provided for receiving a screw. The plate can be tailoredto the required length, which is done by cutting off surplus platemembers, and can be bent to adapt it to the local anatomical situation.

The bone plate and a plate-screw connection have to satisfy thefollowing requirements:

high degree of strength and stability of the bone plate;

high degree of rigidity of the plate-screw connection;

flexibility of the plate in all planes with minimal loss of strengthboth in the plate plane and also around the plate plane, including astorsion;

possibility of applying the various biological tissue types on theplate;

least possible surface pressure of the plate on the periosteum; and

securing (so-called blocking) of the screws passing through the plate inorder to prevent the screws from coming loose.

PRIOR ART

In order to keep the surface pressure of the plate on the periosteum toa minimum, U.S. Pat. No. 5,810,823 proposes arranging spacer elementswith an internal thread which are fixed on or can be fitted onto thelower surface of the plate and which sit on the bone and are passedthrough by the threaded shanks of the screws. Spacer elements whoseposition can be varied also permit an orientation of the screws whichdeviates from the vertical. Although this construction avoids the platepressing on the periosteum over a large surface area, increased pressurenevertheless arises at the points of contact of the spacer elements. Therelatively small spacer elements that can be fitted complicate thesurgical procedure. Regardless of whether the spacer elements are fixedor can be fitted in place, they do not provide any improved securing ofthe screws against their inadvertently coming loose. WO 96/39975describes a blocked plate-screw connection in which recessed securingelements are provided on the lower surface of the plate, which can befitted in the area of the screw holes. The threadless neck portion ofthe screw shank passes through the individual securing element, saidscrew shank having a smaller diameter than the threaded part. Thethreaded part can firstly be passed through the securing element andscrewed into the bone, the screw head coming to lie in a countersink onthe upper surface of the plate. After heat treatment, the securingelement shrinks so that the plate is held at a distance from theperiosteum and the screw is secured against unscrewing. This systemrequires the special securing elements and devices and is thereforeexpensive to manufacture and handle.

The company brochure “SYNTHES®—THORP Reconstruction Set” from STRATECMedical, Waldenburg, Switzerland, discloses a plate system in whichanchoring screws are first screwed through the screw holes of the plateinto the bone. An expansion screw is screwed into the slotted head ofthe anchoring screw which sits in the screw hole. In this way, the headof the anchoring screw presses against the wall of the screw hole in theplate. The anchoring screw is thus secured against unscrewing and theplate is held as it were at a distance from the periosteum. To ensurethat the screw holes in the plate do not narrow upon bending, bendinserts are provided as insertable cores. The relatively large number ofparts means that the operation takes longer and entails moreinstrumentation and is as a whole made more difficult.

A further development of a blockable plate-screw connection is knownfrom U.S. Pat. No. 5,709,686. The bone plate has a plurality of holesprovided in the direction of the longitudinal axis of the plate andintended for the passage of screws. The screw hole is of oval shape, itsmain axis lying in the longitudinal axis of the plate. On the uppersurface of the plate, the screw hole is surrounded by a sphericalcountersink. Over the shorter minor axis of the screw hole there is apartial internal thread whose turns each run out to the main axis of theoval screw hole. The internal thread serves to receive a threadedportion which lies under the head of the screw and which in diameter iswidened compared to the threaded shank of the screw. The screw holeopens toward the lower surface of the plate in the area of both ends ofthe main axis, i.e. outside the internal thread on the longitudinal axisof the plate.

In the clinical application of the plate, the threaded shank of thescrew protrudes into the bone while the threaded portion with theinternal thread engages in the screw hole. The plate is thus supportedand is not pressed by the tensile force of the screw onto theperiosteum. The screw is secured against inadvertent unscrewing by thethreaded connection between the internal thread in the screw hole andthe threaded portion of the screw. Plate and screw are blocked. In theevent of eccentric application of a screw without threaded portion, thecountersink around the screw hole permits a compression between bonecompartments. Screws without a threaded portion for blocking can also bescrewed in in a direction deviating from the vertical. Greater clearancefor this exists in the direction of the longitudinal axis of the plateas a result of the oval hole shape and the only partial internal threadin the screw hole.

The plate-screw connection according to U.S. Pat. No. 5,709,686 permitssatisfactory blocking and an additional securing of the screws, butthere are still serious disadvantages, for example:

To prevent deformations of the internal thread in the screw holes whenbending the plate, bend inserts again have to be used.

Even at low torques when the screw is being screwed in, the internalthread in the screw hole can be overscrewed. With standard screwdrivers,such critical torques can be quite easily applied. A damaged plate isunusable; a new plate has to be used and if appropriate also a newscrew.

In a blocked plate-screw connection, the inserted screws can only bepositioned vertically, which makes it necessary to use exactly verticaldrill guides.

Because of the overall geometry of the plate holes, machining has to bedone from two directions, which makes the plate production moreexpensive.

OBJECT OF THE INVENTION

In view of the stated inadequacies of the blockable bone plates known todate, with secured screws, the object of the invention is to propose animproved blockable plate-screw connection. The aim here in particular isto manage without third parts such as inserts or expansion screws forblocking and bend inserts. The connections are intended to be lesssensitive to overscrewing and angled offset of the screws in relation tothe vertical and the longitudinal axis of the plate. It is desirable,within the plate-screw connection, to obtain a high release torque forthe screws in order thereby to more effectively prevent the screws fromcoming loose. The clinical application is to be made as straightforwardas possible for the operator. It must still be possible to performosteosynthetic bone compression and to use the connection withconventional screws unblocked. Finally, the parts of the connection mustbe able to be manufactured economically in serial production.

OVERVIEW OF THE INVENTION

The further development of the blockable bone plate according to theinvention is based on a bone plate and screws with a blocking threadaccording to the generic type from U.S. Pat. No. 5,709,686. The plateconsists of a plurality of plate members which are connected to eachother via webs. A screw hole is provided in at least some plate members,preferably in each plate member, and is surrounded on the upper surfaceof the plate by a spherical countersink. Provided internally in thescrew hole there is an engagement contour which consists of contourvalleys and adjacent remaining contour peaks partially running in ahorizontal and radial peripheral direction on the wall of the screwhole. The diameter of the countersink for receiving the screw head isgreater than the clear width of the engagement contour. This runs out tothe edges of the engagement contour so that smooth uncontoured wallareas are left there in the screw hole. In relation to the threadedshank of the screw, the screw hole is shaped as an oblong hole. Theengagement contour is preferably produced by milling and has for examplea pointed, round, trapezoidal or serrated configuration.

The screw intended for blocking has, under the screw head, a blockingthread which has the same diameter as or a greater diameter than thethread on the threaded shank which is intended for engagement in thebone. When fixing the plate on the bone, the screw passes through thescrew hole with its threaded shank, and the thread of the threaded shankscrews into the bone. In the final phase of screwing-in of the screw,the blocking thread under the screw head engages in the engagementcontour in the screw hole. As the blocking thread with its helicalcourse and its pitch is not complementary in form to the engagementcontour, deformation occurs on both, resulting in a connection resistantto loosening. A blocking of reduced strength can be obtained if on thescrew there is a complete thread whose uppermost turns run jammedunderneath the engagement contour.

Particular advantages in the osteosynthesis of fractures on curvedbones, for example a lower jaw, are obtained using the blockingaccording to the invention on a bone plate with a plate longitudinalaxis in the shape of an arc of a circle. The bone plate consists atleast of a main segment in the shape of an arc of a circle. For specialpurposes, the main segment is provided with a lateral segment which isattached to it at one end or at both ends and lies in the plate plane,and which lateral segment is straight or curved. Some screw holes on thebone plate can be designed not for blocking, but as cylindrical standardscrew holes or as oriented compression holes. The bone plate in theshape of an arc of a circle preferably acquires its shape withoutforming, so that the plates reach the surgeon without initial weakeningcaused by bending stresses.

By virtue of the invention, a blockable plate-screw connection is nowavailable with the following advantages:

The plate-screw connection is efficient in clinical application since nothird parts are needed for blocking. Also, no bend inserts are neededwhen bending the plate. The plate tends to bend in the area of the websconnecting the individual plate members. However, even in the event ofbending within the screw hole, the function of the blocking is notimpaired.

During blocking, no forces act on the periosteum, so that the latter isprotected. The plate can be positioned at a distance from the bonesimilar to a fixator.

The internal engagement contour in the screw hole also permits a slightangular offset of the inserted screw in relation to the vertical and tothe longitudinal axis of the plate. This is achieved without anyfunctional loss of the blocking.

Upon generation of compression, the screws are not subjected to tensilestress since the blocking of the screw in the plate prevents any axialmovement between plate and bone.

The inserted screws are better protected against inadvertent looseningbecause a high release torque has to be applied. This is due to thedeformations during blocking on the internal engagement contour on thescrew hole and on the associated thread of the screw.

The risk of overscrewing and thus of damage to the plate is reduced. Inconventional plates, the screws are overscrewed even at low insertiontorques which can be applied effortlessly with standard screwdrivers.

The engagement contour arranged internally in the screw holes causessubstantially less notch effect than a conventional internal thread, asa result of which there is less risk of the plate breaking.

The plate can be fitted with different screws, namely those with whichblocking is obtained and those without blocking. In the latter case, thescrew holes function as neutral compression holes for receiving thescrew head. This, for example, for applying small screws in order tofasten a bone compartment. Here, the screw can also be inserted at aninclination.

Since the complete geometry of the screw holes in the plate can beworked from one side, retooling is not required during machining, thusresulting in overall cost-effective production which can also beexecuted with precision at a reasonable cost.

In the configuration of the bone plate with a longitudinal axis of theplate in the shape of an arc of a circle (at least in the main segmentif the bone plate is provided with a lateral segment attached at one endor both ends), after bending the webs out of the plate plane, as it wereover the surface, it is possible to adapt the bone plate closely to thebone. The additional bending in the plate plane is dispensed with, thatis to say the setting or twisting over the edge. By means of thecircular arc-shaped starting geometry, the bone plate assumes theinclination of a circular section of the jacket surface of a cone. Thisreduces the surgical effort when adapting the plate and also reduces thelosses of strength thereof because of minimal deformation. There isideal adaptation of the bone plate in its longitudinal extent and theinclination over the plate width.

BRIEF DESCRIPTION OF THE ATTACHED DRAWINGS

In the drawings:

FIG. 1A shows a bone plate screwed onto a fractured lower jaw;

FIG. 1B shows a bone plate screwed onto the lower jaw for bridging acontinuity defect;

FIG. 2A shows a plan view of a bone plate with uniformly oriented screwholes;

FIG. 2B shows the representation according to FIG. 2A, with differentlyoriented screw holes;

FIG. 2C shows the bone plate according to FIG. 2A in the section alongthe line A—A, with the engagement contour in a first embodiment, outlinesketch;

FIG. 2D shows the representation according to FIG. 2C with theengagement contour, actual contour;

FIG. 2E shows the bone plate according to FIG. 2A in the section alongthe line B—B;

FIG. 3A shows a double-threaded bone screw with blocking thread in theneck area;

FIG. 3B shows the double-threaded bone screw according to FIG. 3A withblocking thread in the neck area and thicker screw shank;

FIG. 3C shows a bone screw with blocking thread in the neck area andself-boring and self-tapping thread on the screw shank;

FIG. 3D shows the bone screw according to FIG. 3C with blocking threadin the neck area and self-boring and self-tapping thread on the screwshank and additional cutting groove;

FIG. 3E shows a single-threaded self-tapping bone screw with pointedthread flanks;

FIG. 3F shows a double-threaded self-tapping bone screw with pointedthread flanks and thicker screw shank;

FIG. 3G shows the double-threaded self-tapping bone screw according toFIG. 3F with rounded thread in the neck area;

FIG. 3H shows the single-threaded self-tapping bone screw according toFIG. 3E with pointed thread flanks, greater pitch and greater externaldiameter on the screw shank;

FIG. 4A shows the bone screw according to FIG. 3A screwed verticallyinto and blocked in a screw hole from FIG. 2E;

FIG. 4B shows the view according to FIG. 4A, with the inserted bonescrew blocked at an inclination;

FIG. 4C shows bone screws according to FIG. 3A screwed into and blockedin screw holes with engagement contours in a first embodiment accordingto FIG. 2E of a curved bone plate;

FIG. 4D shows bone screws screwed into a curved and twisted bone plateaccording to FIG. 2A;

FIG. 5A shows the bone screw according to FIG. 3A with blocking thread,deformed after blocking;

FIG. 5B shows a screw hole with an engagement contour in a firstembodiment from FIG. 2E, deformed after blocking;

FIG. 6A shows a plan view of a screw hole with an engagement contour ina second embodiment;

FIG. 6B shows the view according to FIG. 6A as a section along the lineC—C;

FIG. 6C shows the view according to FIG. 6A as a section along the lineD—D;

FIG. 6D shows the bone screw according to FIG. 3E, screwed into andblocked in the screw hole from FIG. 6B;

FIG. 7A shows a plan view of a screw hole with an engagement contour ina third embodiment;

FIG. 7B shows the view according to FIG. 7A as a section along the lineE—E;

FIG. 7C shows the bone screw according to FIG. 3F, screwed into andblocked in the screw hole from FIG. 7B;

FIG. 8A shows a plan view of a screw hole with an engagement contour ina fourth embodiment;

FIG. 8B shows the view according to FIG. 8A as a section along the lineF—F;

FIG. 8C shows the bone screw according to FIG. 3G, screwed into andblocked in the screw hole from FIG. 8B;

FIG. 9A shows a plan view of a screw hole with an engagement contour ina fifth embodiment;

FIG. 9B shows the view according to FIG. 9A as a section along the lineG—G;

FIG. 9C shows the bone screw according to FIG. 3H, screwed into andblocked in the screw hole from FIG. 9B;

FIG. 10A shows the situation before closure of a fracture by means ofcompression osteosynthesis;

FIG. 10B shows the situation during closure of the fracture;

FIG. 10C shows the situation after closure of the fracture;

FIG. 11A shows a bone screw without blocking thread;

FIG. 11B shows the bone screw without blocking thread according to FIG.11A, with thicker screw shank;

FIG. 11C shows the bone screw according to FIG. 11A screwed verticallyinto a screw hole from FIG. 2E, and not blocked;

FIG. 11D shows the view according to FIG. 11C with the bone screwscrewed in at an inclination and not blocked;

FIG. 11E shows the situation in traction screw osteosynthesis, with abone screw without blocking thread according to FIG. 11A screwed into ascrew hole with engagement contours in a first embodiment according toFIG. 2E, and not blocked;

FIG. 12A shows the bone screw according to FIG. 3E screwed verticallyinto a screw hole from FIG. 2C, and not blocked;

FIG. 12B shows the view according to FIG. 12A with the bone screwscrewed in at an inclination, and not blocked;

FIG. 13A shows a bone plate with a longitudinal plate axis Z in theshape of an arc of a circle and with 16 screw holes;

FIG. 13B shows an enlarged view of three plate members according to FIG.13A;

FIG. 13C shows an outline sketch of a human lower jaw with the fittedcircular arc-shaped bone plate according to FIG. 13A and with a straightbone plate according to FIG. 2A drifting away from the lower jaw;

FIG. 14A shows a bone plate for the left branch of the jaw, with acircular arc-shaped main segment according to FIG. 13A, a straightascending lateral segment, and a strengthened angle area with anadditional screw hole;

FIG. 14B shows the bone plate according to FIG. 14A with a curvedlateral segment and a strengthened angle area without an additionalscrew hole;

FIG. 14C shows the bone plate according to FIG. 14B with an additionalscrew hole in the strengthened angle area;

FIG. 14D shows the bone plate according to FIG. 14A without anadditional screw hole in the strengthened angle area; and

FIG. 14E shows the bone plate according to FIG. 14A with a reducedspacing of the screw holes in the lateral segment.

ILLUSTRATIVE EMBODIMENTS

Referring to the attached drawings, there now follows a detaileddescription of illustrative embodiments of the osteosynthetic bone plateaccording to the invention with blockable bone screws.

The following observation applies to the whole of the description givenbelow. If, for the purposes of clarity of the drawings, referencenumbers are included in a figure but are not mentioned in the directlyassociated text of the description, reference is made to their mentionin preceding or subsequent figure descriptions. In the interests ofclarity, repeated mention of components in subsequent figures is for themost part avoided provided that it is clear from the drawings that theseare “recurring” components.

FIGS. 1A and 1B

These figures show two typical applications of the blockable bone plate1 according to the invention which, together with bone screws 9,constitutes a plate-screw connection. First, the plate 1 is eminentlysuitable for osteosynthesis of a lower jaw which has fractured into bonecompartments (see FIG. 1A). A further principal use lies in the bridgingof a continuity defect, that is to say, where a bone section is missing,the plate 1 has to take up the load permanently and stabilize the lowerjaw (see FIG. 1B). Pressing of the plate 1 on the periosteum andinadvertent loosening of the inserted screws are to be avoided, so thata solid blocking is particularly relevant here.

FIGS. 2A to 2E

In its simplest form, the plate 1 is an elongate linear branch throughwhich the longitudinal axis Z of the plate extends. The plate 1 is madeup of a multiplicity of plate members 2 which are connected to eachother via webs 3. The webs 3 form waist-like transitions betweenadjacent plate members. A screw hole 4 is provided in at least someplate members 2, but preferably in each plate member. On the uppersurface 5 of the plate, the screw holes 4, which open out on the lowersurface 6, are surrounded by a spherical countersink 7. Located insidethe screw hole 4 there is an engagement contour 8.

The engagement contour 8 looks like a partial thread, but only at firstsight; in fact the engagement contour 8 consists of contour valleys 80and alternating adjacent contour peaks 81 arranged on the wall of thescrew hole 4 and extending parallel to the plate plane Y. The contourvalleys 80 and peaks 81 run partially in the peripheral direction in thescrew hole 4, i.e. run out to the edges of the engagement contour 8, sothat uncontoured wall areas 82 are left there in the screw hole 4. Thecountersink 7 has a depth which is such that the screw heads arereceived in a recessed manner. The diameter of the countersink 7 isgreater than the clear width of the engagement contour 8. The distancebetween opposite contour valleys 80 and contour peaks 81 is smaller thanthe distance between the opposite uncontoured wall areas 82, so that theexit 83 of the screw hole 4 on the lower surface 6 of the plate has anoblong hole shape. The contour valleys 80 and contour peaks 81 formingan engagement contour 8 can be arranged substantially parallel to thelongitudinal axis Z of the plate or at an angle thereto, so that thelongitudinal dimension of the exit 83 lies on the longitudinal axis Z ofthe plate (see FIG. 2A) or assumes different angles to the longitudinalaxis Z of the plate (see FIG. 2B). Correspondingly, the uncontoured wallareas 82 are distributed along the longitudinal axis Z of the plate orare offset thereto. In this first embodiment of the engagement contour8, the contour valleys 80 and contour peaks 81 form trapezoidal threads.

FIG. 3A

At its top, the bone screw 9 has the screw head 90 which underneath isdesigned as a spherical cap to complement the countersink 7 in the plate1. Located in the screw head 90 there is a recess 91, for example across slot, into which a screwing instrument can be inserted from above.Located under the screw head 90 there is a blocking thread 92, designedhere as a trapezoidal thread, corresponding to the engagement contour 8.The double-threaded bone thread 94 is arranged along the screw shank 93.The bone thread 94 has, for example, an external diameter of 2.5 mm,while the external diameter of the blocking thread 92 is significantlygreater, for example 3.2 mm.

FIG. 3B

If the diameter, for example 2.5 mm, of the bone thread 94 in thepreceding screw 9 is too small, because the screw hole drilled in thebone is too large or the strength is not sufficient, it is possible touse a modified screw 9 with a greater diameter of the bone thread 94,for example 3.2 mm. Even with this diameter, the bone thread 94 can bemoved effortlessly through the engagement contour 8 in the plate 1. Bycontrast, the wide trapezoidal flanks of the blocking thread 92 resultin a blocking with the engagement contour 8.

FIGS. 3C and 3D

For a blockable plate-screw connection, it is possible as an alternativeto use the self-boring screw 9 shown which likewise has, under the screwhead 90, a trapezoidal blocking thread 92 from which the bone thread 94extends. By way of example, the bone thread 94 has a maximum externaldiameter of 2.5 mm and the blocking thread 92 has an external diameterof 3.2 mm. The screw 9 according to FIG. 3D is additionally providedwith a cutting groove 96 at the tip 95 of the shank.

FIGS. 3E, 3F and 3H

These screws 9 have a continuously uniform thread along the screw shank93, with pointed thread flanks, which thread engages with the suitablycontoured engagement contours 8 in the plates 1, in the upper part asblocking thread 92 and in the lower part as bone thread 94. The screws 9according to FIGS. 3E and 3H are single-threaded, and the screw 9according to FIG. 3F is double-threaded.

FIG. 3G

This shows a double-threaded screw 9 with rounded thread flanks on theblocking thread 92 and pointed thread flanks on the bone thread 94.

FIGS. 4A to 4D

The engagement contour 8 in the plate 1 allows the screw 9 with theblocking thread 92 to be inserted into the screw hole 4 both vertically(see FIG. 4A) and also at an angle a in relation to the longitudinalaxis Z of the plate (see FIG. 4B). Even with the screw 9 positioned atan inclination, fully effective blocking is still achieved; the blockingthread 92 likewise engages in the engagement contour 8. The uncontouredwall areas 82 lying at the ends of the engagement contour 8, with thelongitudinal dimension of the exit 83, offer clearance for the approachof the inclined blocking thread 92. By means of the inclined position ofthe screw 9, the screw head 90 comes to lie obliquely in the countersink7. The in practice complete and seamless bearing of the screw head 90 inthe countersink 7 results from the complementary spherical surfaceslying on each other.

Bending the plate 1 about the plate plane Y (see FIG. 4C) or in theplate plane Y or twisting the plate 1 (see FIG. 4D) does not adverselyaffect the function of the blocking. On the one hand, the main change inthe shape of the plate 1 takes place in the area of the webs 3, and onthe other hand the engagement contour 8, as a result of limiteddeformation, does not lose any of its effectiveness.

FIGS. 5A and 5B

These show the deformation which is caused during blocking between theengagement contour 8 and the blocking thread 92 inserted into thelatter, which deformation secures the screw 9 in a very effective manneragainst inadvertently coming loose. Engagement contour 8 and blockingthread 92 are not complementary to each other. The blocking thread 92has a helically extending thread tooth; or correspondingly, in the caseof a double-threaded thread, two teeth. The engagement contour 8 bycontrast consists of the contour valleys 80 and contour peaks 81 whichdo not extend in a pitch angle, as in the case of a helical thread. Whenthe blocking thread 92 is inserted between the contour peaks 81, thereis a deliberate collision and mutual deformation. The blocking thread 92requires as a supplement helical internal thread turns, and thehorizontally extending contour peaks 81 brace themselves against theinsertion of the blocking thread 92. By means of this contrast theblocking thread 92 and the engagement contour 8 deform, i.e. bothdevelop bend edges 920, 810 which are directed toward each other andwhich abut each other when the screw 9 is unscrewed and thus form aconsiderable resistance to inadvertent loosening. If the screw 9 is tobe unscrewed, a high torque has to be exerted to achieve a partialreturn to shape of the bend edges 920, 810 and to overcome the increasedfrictional resistance. For the engagement contour 8, the preferred rangeof the vertical distance between recurring structures—the contourvalleys 80 or the contour peaks 81—is between 0.5 mm and 1.0 mm. Thecontour valleys 80 can expediently be produced by milling, so that thecontour peaks 81 remain between the milled contour valleys 80.

FIGS. 6A to 6D

The second embodiment of the engagement contour 8 is likewise made up ofcontour valleys 80 and contour peaks 81 which are worked into the wallof the screw hole 4, parallel to the longitudinal axis Z of the plate,and run out at their ends in uncontoured wall areas 82. The particularfeature here lies in the fact that contour valleys 80 and contour peaks81 lie offset in relation to each other on both sides of thelongitudinal axis Z of the plate. In this way the uniform thread on thescrew shank 93 acts in the upper part as a blocking thread 92, whosethread teeth engage behind the contour peaks 81, while the lower partacts as a bone thread 94 for insertion into the bone. The screw head 90with its spherical cap bottom sits in the spherical countersink 7.

FIGS. 7A to 7C

The third embodiment of the engagement contour 8 is made up of contourvalleys 80 and contour peaks 81 which extend inside the screw hole 4parallel to the longitudinal axis Z of the plate and are serrated inshape. Here, the contour valleys 80 and contour peaks 81 lie at the sameheight on both sides of the longitudinal axis Z of the plate and, at theends of the engagement contour 8, run out in uncontoured wall areas 82.The double-threaded screw 9 also used in this plate-screw connection hasa uniform thread along its screw shank 93, the upper part of whichengages as a blocking thread 92 under the contour peaks 81, while itslower part is provided as a bone thread 94 for insertion into the bone.The screw head 90 is again recessed in the spherical countersink 7.

FIGS. 8A to 8C

In this fourth embodiment of the engagement contour 8, the contourvalleys 80 and the contour peaks 81 have a rounded shape. Complementingthe rounded shape of the engagement contour 8, use is made of a screw 9with a double-threaded blocking thread 92 which is designed as a roundedthread. The pointed double-threaded bone thread 94 extends below theblocking thread 92. The rounded contour valleys 80 and contour peaks 81lie at the same height on both sides of the longitudinal axis Z of theplate, with uncontoured wall areas 82 at the ends of the engagementcontour 8. The blocking thread 92 assumes a blocked engagement with thecontour valleys 80 and peaks 81. The screw head 90 is accommodated inthe countersink 7.

FIGS. 9A to 9C

The particular feature of the fifth embodiment of the engagement contour8 lies in the fact that the contour peaks 81 in the screw hole 4 areoffset in relation to each other in the plate plane Y by in each case120° and in height—relative to the plate plane Y—lie in a stairwayconfiguration with respect to one another. Contour valleys and peaks 80,81 have an angular shape. Corresponding to the engagement contour 8, thescrew 9 used has a uniform thread running along its screw shank 93, theupper part engaging as a blocking thread 92 under the contour peaks 81,and the lower part forming the bone thread 94. The spherical countersink7 accommodates the screw head 90.

FIGS. 10A to 10C

The clinical application of the plate-screw connection is illustratedusing the example of compression osteosynthesis. In the startingsituation (see FIG. 10A), that is to say before closing the fracture,bores 100 are formed in the two bone compartments K1, K2 to beconnected, said bores being eccentric in relation to the screw holes 4in the plate 1. The distance between the bores 100 is greater than thedistance between the screw holes 4 in the plate 1, which is positionedover the fracure site with the bone gap X. The screw holes 4 have theengagement contours 8 and countersinks 7.

To close the fracture (see FIG. 10B), screws 9 are introduced throughthe screw holes 4 of the plate 1 and into the bores 100. With the screwheads 90 still protruding, the screws 9 are at first eccentric in thescrew holes 4. As the screws 9 are screwed in further, the bone thread94 penetrates deeper into the bores 100 and the spherical surfaces underthe screw head 90, interacting with the spherical countersinks 7 in thescrew holes 4, effect the successive centering of the screws 9. At thesame time the blocking thread 92 of the screws 9 begins to engage in theengagement contour 8. Upon centering of the screws 9, these are movedtoward each other and in so doing entrain the bone compartments K1, K2with them; the bone gap X begins to close.

In the final position (see FIG. 10C), the screw heads 90 are recessed tothe maximum extent in the countersinks 7 and the screws 9 are centeredto such an extent that the bone gap X has completely closed. The bonecompartments K1, K2 are now pressed against each other. The blocking isproduced between the blocking thread 92 of the screws 9 and theengagement contours 8; the screws 9 are thus secured against comingloose.

FIGS. 11A to 11D

The two screws 19 shown (see FIGS. 11A and 11B) have no blocking thread92. The screw 19 from FIG. 11A, for example with an external threaddiameter of 2.5 mm, is too weak to come into blocking engagement withthe engagement contour 8. In the screw 19 from FIG. 11B with a greaterexternal thread diameter, for example 3.0 mm, an undercutting 97 isprovided below the screw head 90 so that here once again there is noblocking thread 92. These screws 19 without blocking thread 92, in otherwords only with the bone thread 94, can likewise be used together withthe plate 1 which has engagement contours 8 in its screw holes. Blockingdoes not take place here (see FIG. 11C), as may be desired in actualuse. The screw 19 without blocking thread 92 can also be easily used,inserted at an inclination, together with the plate 1 (see FIG. 11D).

FIG. 11E

This view shows a traction screw osteosynthesis with the plate 1according to the invention and with a conventional screw 19 withoutblocking thread 92. The screw head 90 is supported obliquely in thescrew hole 4, and the screw shank 93 penetrates the two bonecompartments K1, K2 which are to be pressed against each other. In theupper bone compartment K1 there is a through-bore 101 of such width thatthe bone thread 94 cannot engage. In the lower bone compartment K2 thereis a bore 100 of reduced diameter in which the bone thread 94 engages.As the screw 19 is screwed in, the lower bone compartment K2 is drawnagainst the upper bone compartment k1. The engagement contour 8 does notfunction here; the thin screw shank 93 passes through said engagementcontour 8 without blocking.

FIGS. 12A and 12B

For the sake of completeness, these two figures are intended toillustrate that small-fragment screws 29, for example with an externalthread diameter of 2.0 mm, can also be inserted into the plate 1vertically or at an inclination. The small screw head 90 lies deep inthe screw hole 4, and the engagement contour 8 remains without function.Such small-fragment screws 29 with a screw shank 93 protruding from theexit 83 and with the bone thread 94 are used for fixing smaller bonefragments.

FIGS. 13A and 13B

This bone plate 1′ has a longitudinal axis Z in the shape of an arc of acircle, with a multiplicity of plate members 2 which are connected toeach other via webs 3. The plate 1′ extends in the unbent startingcondition in the plate plane Y. A screw hole 4, with the above-describedspecial engagement contour 8 for blocking, is provided in each of theplate members 2. The circular arc-shape of the longitudinal axis Z ofthe plate means that between the center axes Z₁ of the webs 3 and thecenter axis Z₂ of the respectively adjacent screw hole 4 there is anoffset β, for example with 1°≦β≧10° and preferably β=2.50°. Between twoadjacent screw holes 4 there is an offset of 2β, for example with2°≦β≧20° and preferably β=5°. It is not imperative that all screw holes4 have the engagement contour 8 for blocking.

Cylindrical standard screw holes or oriented compression holes can alsobe present on the plate 1′ The circular arc-shaped plate 1′ preferablyacquires its shape without forming. Depending on the intended use, theplate 1′ is produced in the required length, or it is brought to thedesired length by cutting off plate members 2 and webs 3. Likewise, thenumber, positioning, spacing and type of screw holes 4 can be chosenaccording to the intended use.

FIG. 13C

This figure illustrates in an outline sketch the direction of extent andthe geometric adaptation of a plate 1 with a straight longitudinal axisZ and of a plate 1′ with a circular arc-shaped longitudinal axis Z,where both plates 1, 1′ are applied to a human lower jaw and, in thefinal bent state, enclosing the lower jaw, extend between the ascendingjaw branches.

The straight plate 1 applied to the left jaw branch drifts, afterbending the webs 3 out of the plate plane Y, that is over the surface,away from the lower jaw. So that this plate 1 encloses the lower jaw, anadditional bending must be carried out in the plate plane Y in each web3—that is over the edge. Only after this does the plate 1 follow thecourse of the lower jaw. Since the latter in principle has no verticalsurfaces, but extends forward apically, subsequent setting or twistingof the plate members 2 is necessary in order to correctly adapt theplate 1 to the jaw bone.

The plate 1′ is more favorably adapted to the jaw bone as thelongitudinal axis Z of the plate extends in the shape of an arc of acircle. The plate 1′ need only be bent at the webs 3 out of the plateplane Y, that is over the surface, in order to bring the plate into theU-shape enclosing the lower jaw. The bending generally takes placeprincipally in the area of the webs 3. The additional bending in theplate plane Y, that is over the edge, and the setting and twisting aredispensed with here.

Because of the starting geometry in the shape of an arc of a circle, theplate 1′, after bending from the plate plane Y, assumes the inclinationof a circular portion of the jacket surface of a cone. In this way, boththe in principle horizontal U-shaped enclosing of the lower jaw in thelongitudinal extent of the plate 1′ and also the close adaptation of theplate 1′ over its width to the apically extending bone are realized. Thestarting geometry in the shape of an arc of a circle greatly reduces thesurgical work for adapting the plate 1′, the plate 1′ adapts ideally tothe lower jaw, and the losses in strength are reduced because of theminimal deformation, only out of the plate plane Y. The positive effectsare obtained particularly if the circular arc-shaped plate 1′ isproduced without forming, so that the plates 1′ reach the surgeon in thecurved geometry but without prior bending.

FIGS. 14A to 14E

This series of figures shows differently modified plates 1′ with alongitudinal axis Z of the plate extending in the shape of an arc of acircle. All the plates 1′ have a circular arc-shaped main segment 10′ towhich a lateral segment 11′ is attached as an extension at the right endor left end or at both ends. The main segment 10′ is here provided forexample uniformly with 16 screw holes 4 suitable for blocking. At thetransition between the main segment 10′ and the lateral segment 11′there is an angled segment 12′ which is strengthened preferably in widthin relation to the webs 3. The angled segment 12′ can be without holes(see FIGS. 14B and 14D) or can have at least one screw hole 4 (see FIGS.14A, 14C and 14E). The lateral segment 11′ can be straight in the plateplane Y (see FIGS. 14A, 14D and 14E) or curved (see FIGS. 14B and 14C).The modification according to FIG. 14E shows a plate 1′ with a circulararc-shaped main segment 10′ and a straight lateral segment 11′ withreduced spacing between the 5 screw holes 4 shown, the angled segment12′ between these having one screw hole 4. In cases where a curvedlateral segment 11′ is provided at one end or at both ends of thecircular arc-shaped main segment 10′, said lateral segment 11′ can havea bend radius different than the main segment 10′.

What is claimed is:
 1. A blockable bone plate comprising: a plurality ofplate members which are connected to each other via waist-like webs andlie on a plate plane in an unbent state; a bone screw hole in at leastsome plate members; one or more bone screws which can be introducedthrough the screw holes for securing the bone plate, wherein each bonescrew has a screw head which is thickened in diameter, a blocking threadsituated below the screw head, the blocking thread having a pitch angle,and a bone thread which extends at least partially over a screw shank,the screw shank having a smaller cross-sectional diameter than the screwhead; and an engagement contour inside the screw hole for blocking ofthe bone plate by the blocking thread provided on the bone screw,wherein the engagement contour comprises contour valleys and adjacentcontour peaks, which are arranged at least substantially horizontallyand partially running peripherally on the wall of the screw hole, inrelation to the plate plane, there is no orientation, as in the thread,between one contour valley and the next contour valley, and between onecontour peak and the next contour peak, the valleys and peaks of theengagement contour do not extend at a pitch angle, and the blockingthread of the bone screw and the engagement contour of the screw holeare not complementary to each other.
 2. The blockable bone plate asclaimed in claim 1, wherein the screw hole has a spherical countersinkon an upper surface of the plate for partially receiving a lower portionof the screw head for centering the bone screw, and having anoblong-shaped hole at an exit on a lower surface of the plate.
 3. Theblockable bone plate as claimed in claim 1, wherein the blocking threadof the bone screw includes at least one thread and can have a geometrydifferent than or identical to the bone thread so the bone thread can beself-boring and/or self-tapping.
 4. The blockable bone plate as claimedin claim 1 wherein the contour valleys and the contour peaks areoriented along a longitudinal axis of the plate or at an angle to thelongitudinal axis.
 5. The blockable bone plate as claimed in claim 1wherein the engagement contour is similar to one of a pointed, a round,a trapezoidal, and a serrated thread.
 6. The blockable bone plate asclaimed in claim 2 wherein the engagement contour runs out at thehorizontally located ends, so that wall areas remain in the screw holeand uncontoured wall areas lie on a theoretical main axis of theoblong-shaped screw hole in the area of the engagement contour.
 7. Theblockable bone plate as claimed in claim 1 wherein the bone screws areconfigured to be inserted into the screw holes vertically or with anangular offset in relation to a longitudinal axis of the plate and theplate plane.
 8. The blockable bone plate as claimed in claim 1 furthercomprising bend edges developed by deformation on the blocking threadand on the engagement contour during blocking and providing increasedsecurity against the bone screw coming loose.
 9. The blockable boneplate as claimed in claim 1 wherein a distance between adjacent contourvalleys and contour peaks is in the range between 0.5 mm and 1.0 mm. 10.The blockable bone plate as claimed in claim 1 wherein the screw holesare configured such that bone screws without a blocking thread can beinserted vertically or obliquely into the screw holes.
 11. The blockablebone plate as claimed in claim 1 wherein the longitudinal axis of thebone plate extending in the plate plane is at least substantially an arcof a circle.
 12. The blockable bone plate as claimed in claim 11wherein, as a result of the arc-shaped longitudinal axis of the plate,an offset of from about 1° to about 10° is obtained between the centeraxis of the webs and the center axis of the respectively adjacent screwhole.
 13. The blockable bone plate as claimed in claim 11 wherein one ormore screw holes is one of a cylindrical standard screw hole and anoriented compression screw hole.
 14. The blockable bone plate as claimedin claim 11 wherein the bone plate further comprises a main segment witha plate longitudinal axis in an arc of a circle, a straight or curvedlateral segment adjoining the main segment at at least one end, thelateral segment extending in the plate plane, and an angled segmentextending in the plate plane between the main segment and the lateralsegment.
 15. The blockable bone plate as claimed in claim 14 wherein theangled segment is strengthened relative to the webs connecting the platemembers and has no holes or has at least one of a screw hole includingthe engagement contour for blocking, a cylindrical standard screw hole,and an oriented compression hole and wherein the lateral segment isprovided with at least one of screw holes having the engagement contourfor blocking, cylindrical standard screw holes, and oriented compressionscrew holes.
 16. The blockable bone plate as claimed claim in 11 whereinthe arc of the bone plate is produced without deforming the bone plate.17. The blockable bone plate as claimed in claim 11 wherein the boneplate is configured for the substantially horizontal, U-shapedengagement of the human jaw bone, in particular the lower jaw, where theends of the bone plate, which consists only of a main segment or of oneor two additional lateral segments, are dimensioned so as to engage overat least one ascending branch of the jaw.
 18. A blockable bone platecomprising: a plurality of plate members which are connected to eachother via waist-like webs and lie on a plate plane in an unbent state; abone screw hole in at least some plate members; at least one bone screwwhich can be introduced through the screw holes for securing the boneplate, wherein at least one bone screw has a screw head, a blockingthread situated opposite the screw head, the blocking thread having apitch angle, and a bone thread which extends at least partially over ascrew shank, the screw shank having a smaller cross-sectional diameterthan the screw head; an engagement contour inside the screw hole forblocking of the bone plate by the blocking thread, wherein theengagement contour comprises contour valleys and adjacent contour peakspartially running peripherally on an inner wall of the screw hole, and,in relation to the plate plane, there is no orientation as a threadbetween one contour valley, and the next contour valley and between onecontour peak and the next contour peak so that the valleys and peaks ofthe engagement contour do not extend at a pitch angle and the blockingthread of the bone screw and the engagement contour of the screw holeare not complementary to each other, the screw hole has a sphericalcountersink on an upper surface of the plate for partially receiving alower portion of the screw head and for centering the bone screw, and isan oblong hole on a lower surface of the plate, and the engagementcontour tapers and is absent at horizontally located ends of the hole,so that uncontoured wall areas of the screw hole lie on a theoreticalmain axis of the oblong hole.
 19. The blockable bone plate as claimed inclaim 18, wherein the blocking thread of the bone screw includes atleast one thread geometrically different from or identical to the bonethread, so the bone thread can be self-boring and/or self-tapping. 20.The blockable bone plate as claimed in claim 18, wherein the contourvalleys and the contour peaks are oriented along a longitudinal axis ofthe plate or at an angle to the longitudinal axis.
 21. The blockablebone plate as claimed in claim 18, wherein the engagement contour issimilar to one of a pointed, a round, a trapezoidal, and a serratedthread.
 22. The blockable bone plate as claimed in claim 18, wherein thebone screws are configured to be inserted into the screw holesperpendicular to or with an angular offset in relation to a longitudinalaxis of the bone plate and the plate plane.
 23. The blockable bone plateas claimed in claim 18, further comprising bent edges developed bydeformation on the blocking thread and on the engagement contour, duringblocking, and providing increased security against the bone screw comingloose.
 24. The blockable bone plate as claimed in claim 18, whereindistance between adjacent contour valleys and contour peaks is in therange between 0.5 mm and 1.0 mm.
 25. The blockable bone plate as claimedin claim 18, wherein the screw holes are configured such that bonescrews without blocking thread can be inserted into the screw holes. 26.The blockable bone plate as claimed in claim 18 wherein a longitudinalaxis of the bone plate extending in the plate plane is at leastsubstantially an arc of a circle.
 27. The blockable bone plate asclaimed in claim 26, wherein as a result of the circular arc-shapedlongitudinal axis of the plate, an offset of from about 1° to about 10°is obtained between a center axis of the webs and a center axis of therespectively adjacent screw hole.
 28. The blockable bone plate asclaimed in claim 26, wherein at least one of the screw holes is one of acylindrical standard screw hole and an oriented compression screw hole.29. The blockable bone plate as claimed in claim 26 wherein the boneplate further comprises a main segment with a plate longitudinal axis inone of an arc of a circle, and a straight or curved lateral segmentadjoining the main segment at at least one end, the lateral segmentextending in the plate plane, and an angled segment extending in theplate plane between the main segment and the lateral segment.
 30. Theblockable bone plate as claimed in claim 29 wherein the angled segmentis strengthened relative to the webs connecting the plate members andhas no holes or has at least one of a screw hole including theengagement contour for blocking, a cylindrical standard screw hole, andan oriented compression hole, and wherein the lateral segment includesat least one of screw holes having the engagement contour for blocking,cylindrical standard screw holes, and oriented compression screw holes.31. The blockable bone plate as claimed claim in 26 wherein the arc ofthe bone plate is produced without deforming the bone plate.
 32. Theblockable bone plate as claimed in claim 26 wherein the bone plate isconfigured for the substantially horizontal, U-shaped engagement of thehuman jaw bone, in particular the lower jaw, where ends of the boneplate, which consists only of a main segment or of one or two additionallateral segments, are dimensioned to engage more than at least oneascending branch of the jaw.